Some have wondered: Why is special counsel Robert Mueller bringing so few charges against George Papadopoulos and, especially, Paul Manafort?

Papadopoulos is easy. Mueller has charged him with one count of false statement, even though there are a dozen other felonies clearly suggested by his plea stipulations. The quick answer is that Papadopoulos has agreed to be a cooperating witness in exchange for a very short sentence. The maximum sentence for false statement is five years. If Papadopoulos cooperates, Mueller can ask for a short sentence, but if he doesn’t, Mueller can add new charges.

Manafort’s case is less obvious. Andrew McCarthy at National Review is puzzled about Mueller’s charges for Manafort, calling it “curious” that he leaves out so many possible charges, including tax fraud and other forms of fraud. “These omissions do not make sense to me,” McCarthy writes. After reading the Papadopoulos plea agreement, and knowing that Manafort is reportedly an unnamed “high-ranking campaign official” in a series of allegedly incriminating emails, one might imagine a dozen other charges Mueller might be mulling.

McCarthy speculates that Mueller did not charge federal tax fraud because those prosecutions require the involvement of the Department of Justice tax division, which would have been an extra bureaucratic hurdle. I’d add that Mueller might have worried that any additional contact with the main DOJ carried a risk of leaks or obstruction. But for the other potential charges, McCarthy writes, “These [other] omissions do not make sense to me.”

Mueller’s moves may make strategic sense because of a shadow hanging over the entire investigation: the potential that President Donald Trump might use his presidential pardon power to protect possible accomplices in potential crimes.

Mueller knows that Trump can pardon Manafort (or any defendant) in order to relieve the pressure to cooperate with Mueller and to keep them quiet. But Mueller also knows that presidential pardons affect only federal crimes and not state-level crimes. On the one hand, double jeopardy rules under the Fifth Amendment prevent a second prosecution for the same crime, but the doctrine of dual sovereignty allows a state to follow a federal prosecution (and vice versa). So in theory, Manafort and Papadopoulos can’t rely on Trump’s pardons to save them even after a conviction or a guilty plea.

But in practice, state rules can expand double jeopardy protections and limit prosecutions. In fact, New York is such a state. New York is the key state for Mueller because New York has jurisdiction over many alleged or potentially uncovered Trump–Russia crimes (conspiracy to hack/soliciting stolen goods/money laundering, etc.), and New York state Attorney General Eric Schneiderman and New York district attorneys are not politically constrained from pursuing charges.

New York’s Criminal Procedure Law 40.20 states, “A person may not be twice prosecuted for the same offense.” The issue is that New York defines “prosecution” broadly. Section 40.30 continues:

Except as otherwise provided in this section, a person “is prosecuted” for an offense, within the meaning of section 40.20, when he is charged therewith by an accusatory instrument filed in a court of this state or of any jurisdiction within the United States, and when the action either: (a) Terminates in a conviction upon a plea of guilty; or

(b) Proceeds to the trial stage and a jury has been impaneled and sworn or, in the case of a trial by the court without a jury, a witness is sworn.

The New York statute does not allow a state prosecution to follow a federal prosecution (“a court of any jurisdiction within the United States”) for the same basic facts. The bottom line: If Mueller starts a trial on all of the potential charges, and then Trump pardons Manafort, Mueller will not be able to hand off the case to state prosecutors. And thus he would have lost leverage at the time of the indictment if he seemed headed toward losing the state prosecution as a backup.

Instead, Mueller wisely brought one set of charges (mostly financial crimes that preceded the campaign), and he is saving other charges that New York could also bring (tax fraud, soliciting stolen goods, soliciting/conspiring to hack computers). Mueller also knew that his indictment document on Monday would include a devastating amount of detail on paper without relying on any witnesses to testify, showing Mueller had the goods on a slam-dunk federal money laundering case. Then he dropped the hammer with the Papadopoulos plea agreement, showing Manafort and Gates that he has the goods on far more charges, both in federal and state court.

Papadopoulos conceded that Russian representatives told him they had “dirt,” in “thousands” of Clinton’s emails in April 2016. It is clear—depending on what Papadopoulos has told them—that prosecutors could start building a case of conspiracy and solicitation of illegal hacking and trafficking in stolen goods against campaign officials Papadopoulos may have informed as well.

I discussed some of the parallel state felony charges in this Slate piece (also published in Just Security). In August, sources revealed that Mueller was already coordinating with Schneiderman, likely to work out this strategy. I also noted that all of this legal background is relevant to solve an additional problem: If Trump fires Mueller, state prosecutors can carry on with his investigation and prosecutions based on parallel state laws.

This same strategy adds an explanation for the single Papadopoulos charge. I explained above that a single charge is a classic part of plea deal for cooperation. But Mueller can be saving a number of other charges, both in his own back pocket to incentivize cooperation and also for the front pockets of state-level prosecutors in case Trump gives Papadopoulos a blanket pardon. Mueller is a stone-cold professional.